Over the years, much effort has been expended in designing industrial filters, such as horizontal plate filters, in such a way as to minimize migration of filter aids and particulates through the filter media used in the filters. The presence of such highly abrasive particulates in a coolant delivered to precision machines, such as rolling mills or the like, is highly detrimental to the machines themselves and also to the resultant quality of the products made from the machines. In a large measure, these efforts to prevent particulate migration to the filter medium have been successful to the point that, in a well designed filtration, system, migration of particulates through the filter media is no longer considered to be a problem during normal operation. Recent investigations, however, have shown that coolant delivered to the process machinery coupled to a filtration system during the period of filter cleaning or blowdown contains particulate materials which are higher in concentrations than that which the in-line filter itself delivers to the machinery.
Further analyses and field inspections of standard divided liquid storage tanks of a system of this type leads to the conclusion that residual particulate materials are returned to the dirty tank portion of the storage tank during blowdown cycles, thence, over the partition dividing the dirty tank from the clean tank, and then on to the process machinery. The result is excessive wear to the machinery and the degradation of the quality of the products made with the machines.
Because of this problem, a need has arisen for apparatus and a method for isolating filter blowdown liquid from the main tankage system to prevent the carryover of residual particles to the process liquid during the time in which the filter is off-line for cleaning or for filter replacement purposes.